About This Item
Share This Item
The Basement Rock project of the A.A.P.G. was initiated in the fall of 1956; it is supported from the Research Fund. The Basement Project Committee, organized on a geographic basis, is currently compiling a basement map of North America between 24° and 60° N. Latitudes. This map will consist of two parts: (1) a map showing basement wells with code number, outcrops of basement rocks differentiated as to age and gross lithology, and contours on the basement surface and (2) a geologic and structural map of the basement. Preliminary copy for (1) is nearly complete. This map will be published through the cooperation of the U. S. Geological Survey and will be accompanied by a text giving basic data for all wells.
Basement studies are important in regional evaluations. Knowledge of basement geology and structural grain aids in interpretation of geophysical data. Movements along basement structures produce structures in younger basin rocks which can be prospected more effectively if the basement control is recognized. Basement topography controls the facies of overlying sedimentary rocks. A regional knowledge of basement terranes is valuable in determining source of sediments and direction of transport. In areas where basement rocks are not "granite," thousands of unnecessary feet of hole have been drilled into metasedimentary and volcanic rocks. In some areas fractured basement rocks are reservoirs.
Petrographic methods, supported by geophysical and other information, can, within the limits of well control, establish (a) major lithologic and tectonic features such as orogenic belts, volcanic terranes, plutonic terranes, and fault zones and (b) tectonic divisions within concealed orogenic belts, such as allocthonous plates, belts characterized by different type and degree of metamorphism, and zones of igneous activity.
End_of_Article - Last_Page 1249------------